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Biomedical subjects

M Shea

Publications and source records attributed to M Shea.

At least 19 recordsLinked to original sources
PubMed1992

Effects of 4-amino-1-hydroxybutylidene bisphosphonate on bone biomechanics in rats.

Bisphosphonates inhibit osteoclast-mediated bone resorption, but their effects on the mechanical behavior of bone remain uncertain. This study investigated the effects of 4-amino-1-hydroxybutylidene bisphosphonate (AHBuBP) on the biomechanical and morphologic properties of bone in ovariectomized rats. Sprague-Dawley rats (four groups, n = 6) were ovariectomized at 3 months of age. From 7 to 13 months, the groups received vehicle or 0.28, 2.8, or 28 micrograms/kg of AHBuBP twice weekly through subcutaneous injection. An additional group of control animals (n = 6) received neither surgery nor drug. We determined the stiffness, yield, and ultimate loads of the femoral midshaft, the sixth lumbar (L6) vertebra, and the femoral neck. Geometric properties of the cortical bone were measured from digitized images of the tibial diaphysis at the level of the synostosis. The area fraction of trabecular bone was determined through the midsagittal plane of the fifth lumbar (L5) vertebra. There were no significant differences in the structural properties of the femoral neck and midshaft, with the exception that the medium-dose group had a greater ultimate load than the vehicle group for the femoral midshaft in bending. Cross-sectional analysis of the tibia did not show significant differences in the inertial properties or area. Ovariectomy caused a significant reduction in the stiffness and ultimate load of L6 and in the area fraction of trabecular bone of L5.(ABSTRACT TRUNCATED AT 250 WORDS)

Alendronate↗
PubMed1992

In vitro hyperextension injuries in the human cadaveric cervical spine.

To investigate the relationship between the type of hyperextension injuries and the conditions producing them, nine cervical specimens (occiput to T1) were loaded to failure in tension at a fixed extension angle of 30 degrees. Under these loading conditions, specimens failed at average tensile loads and extension moments of 499 +/- 148 (SD) N and 4.0 +/- 3.1 Nm, respectively. Failure occurred at an average tensile displacement of 18.8 +/- 7.7 mm. The anterior longitudinal ligament ruptured and the intervertebral disc failed in at least one level in all specimens. In four specimens, the disc failed at an additional level, leaving the anterior longitudinal ligament intact at that site. With one exception, all injuries occurred in the lower cervical spine (C5-C6 and C6-C7), the region most often injured in vivo. The location of the injuries was associated with the degree of degeneration of the facet joints and the discs. The discs of the lower cervical spine were significantly more degenerated than those at the C2-C3 level. In addition, the degree of disc degeneration in the noninjured discs was significantly less than in the injured discs. These data help quantify the threshold of injury and the patterns of tissue damage resulting from hypertension loading of the cervical spine.

Aged↗
PubMed1992

A biomechanical study of the fatigue characteristics of thoracolumbar fixation implants in a calf spine model.

Clinical failures of internal fixation implants for the treatment of the thoracolumbar spine are generally attributed to fatigue. Few studies, however, have characterized changes in fixation rigidity with time or subjected spine-implant fixation constructs to fatigue loading until failure. Fatigue characteristics of five dorsally applied spinal fixation implants were determined using lumbosacral calf spines, with an L3 vertebrectomy, loaded cyclically in combined compression (maximum 605 N) and flexion (maximum 16 Nm) for up to 100,000 cycles. Displacement transducers monitored motion at the site of instability and at the segment above the implants. Flexibility and strain at these segments were then calculated. A one-way analysis of variance showed that there were no significant differences in flexibility of the five fixation constructs (P greater than .05). A multiple Bonferroni test revealed that the AO and Kluger fixateur interne and Steffee plates, with fixation at L2 and L4, allowed significantly more strain (P less than .01) across the site of instability than did Harrington rods and Luque plates with fixation at L1, L2, L4, and L5. There were no significant differences between fixation constructs in initial strain above the implants. After 10,000 cycles, however, there were significant increases in strain across the segment above the Luque and Harrington implants (P less than .05). Failure of the AO Schanz screw occurred in three of six constructs at a mean of 73,300 cycles. The Steffee screws failed in four of five constructs at a mean of 20,800 cycles. The rods of the Kluger fixateur interne broke in four of five constructs at a mean of 47,800 cycles, and one screw slipped at 11,000 cycles. There were no metal failures in the Harrington or Luque implants.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Cyclosporine in the treatment of nonmicrobial inflammatory ophthalmic disease.

Eighteen patients with severe, progressive nonmicrobial inflammatory ophthalmic disease (including five with intermediate uveitis, four with sympathetic ophthalmia and three with serpiginous choroiditis) that had not responded to conventional therapy were treated with cyclosporine. Three of the four patients with sympathetic ophthalmia responded quickly and maximally, and the fourth showed partial improvement. One patient, with several corneal graft failures in the right eye, started cyclosporine therapy after undergoing left corneal transplantation; at the last follow-up visit the graft had been clear for almost 3 years. The response was inconsistent in patients with other types of eye disease. In general, the drug was well tolerated; however, two patients stopped treatment because of unpleasant side effects. No serious or irreversible complications developed. The results suggest that cyclosporine therapy is useful in the treatment of sympathetic ophthalmia and in high-risk corneal transplantation.

Adolescent↗
PubMed1991

Physical and mechanical properties of calf lumbosacral trabecular bone.

The physical and mechanical properties of calf lumbar and sacral trabecular bone were determined and compared with those of human trabecular bone. The mean tissue density (1.66 +/- 0.12 g cm-3), equivalent mineral density (169 +/- 36 mg cm-3), apparent density (453 +/- 89 mg cm-3), ash density (194 +/- 59 mg cm-3), ash content (0.6 +/- 0.05%), compressive strength (7.1 +/- 3.0 MPa) and compressive modulus (173 +/- 97 MPa) of calf trabecular bone are similar to those of young human. There were moderate, positive linear correlations between apparent density and equivalent mineral density, ash density, and compressive strength; and between compressive strength and equivalent mineral density (R2 ranging from 0.35 to 0.48, p less than 0.001). Apparent density, ash density, and equivalent mineral density did not differ significantly in different regions. In contrast to humans, the compressive strength increased from posterior, near the facet, to the anterior vertebral body. These comparisons of physical and mechanical properties, as well as anatomical comparisons by others, indicate that the calf spine is a good model of the young non-osteoporotic human spine and thus useful for the testing of spinal instrumentation.

Animals↗
PubMed1991

Variations of stiffness and strength along the human cervical spine.

The load-displacement response and strength of the mid (C2-C5) and lower (C5-T1) cervical regions were determined for combinations of sagittal loads, in vitro. In unpaired t-test comparisons, the mid cervical region was significantly stiffer in compression and extension than the lower region. In tests to failure, failure in six out of seven mid cervical specimens resulted from flexion alone, while combined compression-flexion was required to fail five of the eight lower cervical specimens. Post-test dissections revealed no regional differences in the pattern of failure. In addition to sagittal tests, the load-displacement responses of three-vertebrae cervical specimens were measured with the upper body axially rotated with respect to the lower body. The effect of this pre-torsion was to diminish the zone of low slope near zero load for axial, shear, and flexion motion. Three of the four axially rotated specimens failed in flexion without added compression. These controlled load-displacement measurements of cervical spine specimens describe for the first time the continuous flexion-compression response up to failure, and suggest that consideration of the biomechanics of three apparently distinct mobile regions of the cervical spine (C1-C2, C2-C5, C5-T1) may facilitate the interpretation of hazardous conditions and the diagnosis of injury. These data also provide basic information for the in vitro investigation of passive cervical spine protection such as helmets and head-rests, suggesting that the head should be kept in a non-rotated position to reduce risk of injury.

Biomechanical Phenomena↗
PubMed1991

Three-dimensional load displacement properties of posterior lumbar fixation.

Pedicular fixation devices for the posterior treatment of segmental spinal instability are thought to offer enhanced stabilization compared with sublaminar wire systems, while avoiding the immobilization of multiple normal motion segments. We compared the performance of three dissimilar stabilization systems: the Hartshill rectangle, the Acromed/Steffee interpedicular screw and plate, and the Synthes/Dick fixateur interne. Human cadaveric lumbosacral specimens were first tested intact, then after a laminectomy and a facetectomy at the L3/L4 level, and finally after the fixation devices were sequentially attached. Constructs spanning two to four vertebral levels were compared for stabilization of the resected lumbar spine segments. When tested in compression, the Acromed/Steffee system with pedicular screws at L2-L5 allowed significantly less intersegmental distraction than the Synthes/Dick construct with screws at L2 and L5 only, and less than the intact and the destabilized uninstrumented spine. When sagittally rotated, the Acromed/Steffee construct with screws at L2-L5, or at L2 and L5, allowed significantly less distraction than the intact or destabilized segments, and the construct with screws at L2 through L5 allowed less distraction than the Synthes/Dick constructs with screws at L3/L4 or L2/L5. With the exception of the Acromed/Steffee system with screws at four levels, there were no significant differences in distraction allowed between the Synthes/Dick and Acromed/Steffee constructs, or between the multisegment and single segment constructs. There were no significant differences in stiffness across levels L3/L4 with the various implants. Results indicate that the use of posterior spine constructs significantly augment the stability of posterior segmental defects. Pedicular fixation immediately cephalad and caudad to the defect provided stable fixation in this application.

Bone Plates↗
PubMed1991

Importance of bone mineral density in instrumented spine fusions.

The effect of equivalent mineral density on pedicular screw fixation strength was investigated. The equivalent mineral density of human vertebral bodies was correlated highly with the pullout force of Kluger screws (r2 = 0.61, P less than 0.02). A moderate to high correlation existed between density and vertical force (r2 = 0.42 for Kluger screws, r2 = 0.55 for Steffee screws, P less than 0.02). In calf vertebral bodies of higher density (146 +/- 14 mg/cc), the forces were significantly higher than in the human vertebral bodies (P less than 0.05). Human lumbosacral spines were instrumented with three different fixators: Steffee plates, AO fixateur interne, and Kluger fixateur interne. Of five specimens with a mean density of 88 +/- 11 mg/cc, one screw loosened. More than one screw loosened in six specimens with a mean density of 63 +/- 12 mg/cc, and no screw loosened in four specimens with a mean density of 114 +/- 38 mg/cc. Measurement of equivalent mineral density correlates with the fixation strength of the intrapedicular screws in vitro and should be considered in patients with signs of osteopenia before using pedicular screws for spinal fusions. It is also concluded that calf spines are a good model for testing implants because they tend to focus failure processes in the implant rather than in the implant-bone interface.

Aged↗
PubMed1991

Importance of freezing time when iodoantipyrine is used for measurement of cerebral blood flow.

The goal of the present study was to determine effects of delay of freezing of the brain on distribution of [14C]iodoantipyrine in the brain. Blood flow to parietal cerebral cortex (CBF) and choroid plexus was measured with the indicator fractionation technique and quantitative autoradiography. After injection of iodoantipyrine, each rat was decapitated, and the head was immersed in chlorodifluoromethane (-40 degrees C). The brain was removed from the skull after it was frozen. In some rats, heads were immersed immediately after decapitation, and CBF was markedly heterogeneous. In another group, heads were frozen 3 min after decapitation. In this case, CBF was uniform in its distribution. Average CBF was similar in groups with immediate and delayed freezing (90-104 ml.min-1 x 100 g-1). In contrast, delays in freezing decreased blood flow to choroid plexus from 551 +/- 115 to 261 +/- 48 ml.min-1 x 100 g-1. Our findings indicate that immediate freezing of the brain after decapitation is necessary to prevent diffusion of iodoantipyrine from regions of high blood flow to regions of lower blood flow and underestimations of blood flow in regions with high blood flow.

Animals↗
PubMed1990

Diagnosis and control of neonatal losses in sheep.

Perinatal mortality is affected by a variety of management factors and disease processes that create significant losses for the sheep industry. Annual production losses prior to weaning include roughly 15% to 20% of the lamb crop. The majority of these perinatal losses occur during the prenatal, natal, and early postnatal periods, with the predominant wave of mortality occurring during the first several days following birth. Causes of perinatal mortality may vary between flocks and between geographic areas; however, four dominant categories of lamb loss consistently surface: (1) abortions; (2) hypothermia, starvation, and exposure; (3) pneumonia; and (4) stillbirth and dystocia. They account for roughly 50% to 75% of all documented perinatal losses. Veterinarians and producers need to work together to document the type of losses that occur in a given flock and then design economic prevention programs that address these problems. In most cases, traditional prevention programs will need to be replaced by a comprehensive management scheme addressing nutrition, genetics, housing, marketing, lambing husbandry, and labor.

Abortion, Veterinary↗
PubMed1990

Compressive strength of autologous and allogenous bone grafts for thoracolumbar and cervical spine fusion.

The selection of the bone graft type for stabilization of spinal fusion depends on availability, the clinical situation, and the desired mechanical stability. The authors determined the potential immediate postoperative compressive strength of various types of bone grafts under axial compression on a material testing machine. The fibular strut graft (5,070 +/- 3,250 N, mean +/- standard deviation [SD]) was significantly stronger (P less than 0.05) than the anterior (1,150 +/- 487 N) and posterior (667 +/- 311 N) iliac crest grafts, and the rib grafts (452 +/- 192 N). Hydroxyapatite grafts with a pore size of 200 mu were significantly stronger (P less than 0.05) than those with a pore size of 500 mu (1,420 +/- 480 N versus 338 +/- 78 N). Ethylenoxide sterilization had no significant effect on the immediate compressive strength. Bicortical and tricortical Bailey-Badgley and Cloward bone grafts also were compared. Results showed that all cervical graft types may be sufficiently strong to support sizable loads.

Aged↗
PubMed1989

Nanophthalmos in sisters, one with exfoliation syndrome.

In a consanguineous family of two siblings, both with nanophthalmos, one was found to also have bilateral exfoliation syndrome. This combination of conditions has not, to our knowledge, previously been reported and has not had any apparent negative consequences. Her sister has manifested typical complications of nanophthalmos, including angle-closure glaucoma initially and, eventually, severe uveal effusion after cataract surgery.

Aged↗
PubMed1988

The role of echocardiography and CT in the diagnosis of cardiac tumors.

A young male who presented with atypical chest pain was found to have a primary cardiac tumor. Chest X-ray, electrocardiogram, and echocardiographic findings can be nonspecific. Differential diagnosis and the role of different diagnostic modalities including echocardiogram, computerized tomography and magnetic resonance imaging are discussed.

Adult↗
PubMed1987

Sequential infusional 5-fluorouracil followed by concomitant radiation for tumors of the esophagus and gastroesophageal junction.

Thirteen patients with esophageal or gastroesophageal tumors with regional disease only were treated with sequential combined therapy. Weeks 1 to 6 continuous (24 hours) infusion 5-fluorouracil (5-FU) 300 mg/m2/d; weeks 6 to 10 or 12 infusional 5-FU administered concomitantly with radiation to the primary tumor site using standard fractionation with a cumulative median dose of 5000 rad; range 4400 to 6900 rad. Surgery was performed in five patients. All patients were evaluable for assessing response to the initial 5-FU infusion and 11/13 patients demonstrated tumor regression. Of 12 evaluable patients subsequently receiving combined infusional 5-FU and concomitant radiation, all 12 achieved complete clinical (10) or pathologic (two) tumor regression. Two of five patients having surgical resection had no pathologic evidence of tumor. All patients had relief of dysphagia within 1 week of initiating chemotherapy. Acute complications of therapy included stomatitis (two patients); hand-foot syndrome (two patients), and subclavian vein thrombosis (two patients). Stricture requiring periodic dilation occurred in three patients, and one patient developed a tracheoesophageal fistula at 36 months. Local control was maintained in 12/13 evaluable patients. Four of 13 patients were alive and without disease at 12 to 46 months. Nine patients died of distant metastases at 6 to 40 months. Median survival for the whole group was 16 months. Ten of the 13 patients (77%) survived for more than 1 year and 3/13 (22%) survived more than 3 years. This pilot study demonstrates the activity of 5-FU administered on an infusion schedule in both squamous and adenocarcinoma of the esophagus and the capacity to deliver infusional 5-FU throughout standard fractionation radiation. The local control and survival data may provide a basis for expanded Phase II trials, and a comparative trial against surgery alone might also be justified.

Aged↗
PubMed1979

The surgical management of macular pucker.

Contractions of collagenous membranes in the posterior cortical vitreous may produce macular pucker and loss of central vision. It is possible to separate these membranes from the retina, and if one succeeds in doing so there is reasonable improvement in central visison. Between December 1976 and September 1978, six patients with macular pucker were operated upon. The clinical details and results are described. The technique used was that of Machemer with the modifications demanded by use of the Klöti vitreous stipper. Several different instruments were used for dissection, the most useful being the joint knife used in stapedectomy.

Cataract↗